Project proposals MENA3100
Energy is likely to be the major scientific challenge in decades to come. The solution to the
climate and environmental problems rests on a concerted effort to broaden our energy
resources. New and improved functional materials are important components in efforts to
effectively harvest energy from alternative energy sources, and to use the available energy
more economically and environmentally friendly.
P1: Characterization of a solar cell with Si2N3 anti reflection coating
Energy relevance: Solar cells have within the last few years become an interesting and
competitive technology to meet the future demands of energy consumption based on
renewable energy sources. The technology of today is based on silicon, and although
alternative materials/methods have been suggested, Si based solar cells will be the leading
technology for years to come. Huge research efforts are therefore put down in
understanding and improving solar cells.
The challenge: The efficiency of a solar cell depends on its electrical characteristics, which
again depends on the impurity types and concentrations in the material. Both intentional
dopant atoms and unintentional impurities can have a large impact on the performance of
the device. It is therefore necessary to characterize the impurities in the device down to a
ppm and ppb range.
Assignment: Characterize a polysilicon solar cell, consisting of a top nitride layer and bulk
silicon, regarding the most prominent impurity elements.
Interesting output is:
- surface morphology/topography
- identification of the most prominent impurity elements
- Depth profiles of the most prominent impurities (down to ppm or ppb)
- Lateral distribution of a few selected impurities
P2: Characterization of a solar cell with an ITO coating doped with Ge
Energy relevance: Typical applications of ITO-coated substrates include touch panel
contacts, electrodes for LCD and electro chromic displays, energy conserving architectural
windows, defogging aircraft and automobile windows, heat-reflecting coatings to increase
light bulb efficiency, gas sensors, antistatic window coatings, wear resistant layers on glass,
etc. ITO films are also widely used, amongst other transparent conductive oxides (TCO) as
both antireflection coatings (ARC) and as transparent conductive electrodes for Si based
solar cells due to their promising performance in terms of electrical conductivity and
transparency in visible light.
The challenge: Creation of nanocrystals – quantum dots is expected to increase the
efficiency of the material in energy conversion. It is therefore important to identify the
chemical state of all species present in the ITO films in order to confirm the presence or
absence of nanoparticles with different chemical state than the matrix.
Assignment: Characterise the structure and chemistry of the films. Where is Ge located
(near surface, bulk or at substrate/film interface). How does the composition of the film
vary with depth. What is the chemical state of In, Sn and Ge and how this varies with
depth?
P3: Thin film of TCO (In2O3:Sn) with In-precursor In(acac)3
P4: Thin film of TCO (In2O3:Sn) with In-precursor InI3
Energy relevance: Thin films of transparent conducting materials are relevant for next
generation solar cells where the anti reflection coating acts both to increase the solar
radiance towards the cell, but also as an active electrode. The ultimate goal is to replace the
metallic conduction bands used today with a transparent material.
The challenge: In order to ensure good properties it is necessary to have well defined
crystalline material that conducts well. We have produced such materials using atomic
layer deposition (ALD) technique with two different processes for the introduction of In
(In(acac)3 precursor in P3, and InI3 in P4).
Assignment: Characterise the material with the aim to obtain structural data (crystallinity
/grain size/texture/phase identification), chemical composition/variations, chemical states
and topography of the films.
P5: ZnSb, thermoelectric material
P6: Zn4Sb3, thermoelectric material
Energy relevance: One component in the new energy landscape will be thermoelectric
materials to produce electricity from waste heat, and as efficient solid state refrigerators
and heat-pumps. The technology based on thermoelectricity produces no harmful or
greenhouse gas emission.
The challenge: The bottleneck with respect to the utilization of thermoelectricity is the
thermoelectric material that needs be a good conductor of electricity and a poor conductor
of heat. In addition, a thermoelectric material is better when a comparatively large voltage
is set up at a given temperature difference between the two ends of the material (large
Seebeck coefficient), or vice versa a comparatively large temperature difference is set up
when electrical current is sent through the material. Among the most promising
thermoelectric materials are compounds of Zn and Sb.
Assignment:
Characterize the material with respect to microstructure and composition variations.
Interesting output, in particular to assess the thermal conductivity of your material, is:
crystal grain size and shape, and possible additional phases.
P7: LaNbO4+LSM composite electrode material, after sintering
P8: LaNbO4+NiO composite electrode material, after sintering
Energy relevance: SOFC (solid oxide fuel cells) based on high temperature proton
conducting electrolytes are very interesting devices to head towards a cleaner way to
produce energy. LaNbO4 is a good candidate for use as electrolyte in such fuel cells, but
we must also find compatible electrode materials to build up a complete button.
The challenge: High polarization resistances from the cathode (P7) or the anode (P8)
contribution are dependent on a number of variables: appropriate porosity of the electrode,
formation of secondary phases or bad adherence, among others.
Assignment: Characterise the microstructure of the composite electrode material with
respect to composition and structure on all levels.
Interesting output is: grain size, how are the connections between grains, porosity,
composition and structure of each phase (LaNbO4 + LSM or NiO), description of the
interface between the two phases (general aspect, interdiffusion, secondary phases etc.)
P9: Locating SiO2 in polycrystalline BaZr0.9Y0.1O3-δ
Energy relevance: Ceramic ionic conductors are interesting materials for applications such
as fuel cells, electrolysers and sensors. A proton conductor is a vital building block in a fuel
cell. BaZr0.9Y0.1O3-δ is a promising electrolyte for high temperature proton conducting fuel
cells, but an especially high grain boundary resistance must be decreased before realization.
The challenge: The high resistance is often attributed to blocking impurities located in the
grain boundaries. 5 samples with increasing amount of added SiO2 have been characterized
electrical giving resistances inconsistently with amount of SiO2. In the present project you
should study the sample with the highest SiO2 concentration (~1 at %).
Assignment: Characterise the material with respect to structure, grain size and the location
and concentration of SiO2. Is SiO2 located at the surface, along grain boundaries or in tipple
points? Are there other elements present in the sample as impurities?
P10: Co3O4 nanocrystals
Energy relevance: Nanomaterials based on cobalt oxide are interesting as cathode
materials in lithium batteries. In addition, controlled assembly of monodisperse and
facetted nanocrystals will be of interest e.g. in connection with development of new
electronic devices and magnetic sensors.
The challenge: It is possible to synthesize monodisperse, non-agglomerated, well facetted
nanocrystals using e.g. hydrothermal methods. One example is Co3O4, a mixed valence
oxide with a spinel type structure. We have synthesized nanocrystals with sizes down to 5
nm, having a cube-like morphology.
Assignment: Characterise the atomic and electronic structure of the phase. Identify the unit
cell and determine the unit cell parameters. Determine the oxidation states of cobalt.
Determine the size of the crystals and determine the crystallographic morphology, i.e. index
the crystal facets. Investigate a 2-dimensional assembly of nanocrystals in order to
determine packing preference, distances etc.